High-efficiency broadband photonic crystal fiber metalens with a large numerical aperture

Photonic Crystal Fiber (PCF), as a novel optical fiber, is widely used in the applications of dispersion control, supercontinuum generation, fiber sensing, etc. However, the numerical aperture (NA) of most PCFs is normally too low to obtain a high coupling efficiency, and the transmitted light is easy to diverge, which limited the applications of PCFs. In recent years, the rapid development of metasurface optics provided an unparalleled platform for improving the optical properties and functionality of the PCFs. Here, we designed two PCF devices integrated with the metalens operating in the telecom region on the basis of numerical simulation, namely PCF divergent metalens (PCF-DM) and PCF focusing metalens (PCF-FM). The simulation results demonstrated that the proposed devices can increase the NA of a PCF from less than 0.1 to 0.65 with coupling efficiencies as high as 90% and 85% through shaping the wave front of the incident light. Meanwhile, it is found that PCF-FM can enhance the focusing capability of a PCF and leads to a focus with a size near the diffraction limit, moreover maintaining a high focusing efficiency. Therefore, we anticipate that the reported novel design would contribute to researches of fiber imaging/sensing, fiber laser, and other PCF-based devices.